helpers

Use this method to define Meteor collections that will be reactive throughout the entire reactive context life.

The parameter of this method is an object whose keys will be added to the reactive context as arrays, representing the
reactive collections. Each value of the object must be a function that returns a Mongo.Cursor.

Under the hood, each helper starts a new Tracker.autorun to create the
reactivity.

The helpers method is part of the ReactiveContext, and available on every context and
$scope and will stop automatically when when it's context ($scope) is destroyed.